Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR APPLYING ULTRAFINE PHOSPHATE CONVERSION CRYSTAL
COATINGS
FIELD OF THE INVENTION
The present invention relates to a phosphate conversion coating and, more
particularly, to a method of applying ultrafine phosphate conversion crystal
coating. The
present invention relates to the method of applying ultrafine zinc, manganese
and calcium
phosphate conversion coatings (PCC) (as well as other materials) on various
metals, alloys
and non-metals.
Phosphate conversion coating, and especially Zinc, Manganese, Iron, Calcium
to phosphate and combination conversion crystal coatings, are used as a
base for improving
adhesion of paints and different organic, silicon-organic and composite
coatings, rubber
moldings etc. In addition, zinc phosphate coating is applied to increase
corrosion protection
of metals, where the coating acts as a carrier for specific oil and wax films
that are applied
over it.
BACKGROUND OF THE INVENTION
An excellent overview of the present state of the art of PCC and in particular
Zinc
Phosphating process is presented in article by John Donofrio. The article
discloses the
following:
"Zinc phosphate is a crystalline conversion coating that is formed on a metal
substrate, utilizing the chemical reaction between metal ions that have been
dissolved in
mineral acids and then diluted with water to form the process solution. The
mineral acids
that are normally used to dissolve the metal ions are nitric acid and
phosphoric acid. Metals
such as Zinc, Nickel and Manganese are dissolved depending on the process
necessary.
Accelerators may be added to the phosphating process to increase reaction
speed, modify
hydrogen elimination and control sludge formation.
Three primary reactions take place:
The first reaction that occurs when the zinc phosphate solution comes into
contact
with the metal surface is the pickling reaction, in which some metal is
dissolved from the
surface. In this reaction, a chemical cleaning of the surface takes place.
This cleaning affects
the adhesion of the coating to the base metal. The free acid of the solution
close to the metal
surface is consumed because of the dissolution of the metal surface. Metal
ions are
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transferred into the process solution. The type of metal depends on the type
of substrate mix
being treated.
The second reaction is the coating reaction. Due to the free acid consumption
in the
liquid-metal interface, pH rises and the metal cations cannot stay soluble in
the solution.
They react with the phosphate in the solution and deposit on the metal surface
as crystalline
Zinc Phosphate.
The third reaction is the sludge reaction. The metal ion (Fe++) that dissolved
from
the pickling reaction is oxidized using the accelerator and precipitate out as
sludge. The
sludge, created in the process, is normally filtered from the solution
utilizing some sort of
filter media or equipment.
Special prerinses, applied to the metal surface prior to phosphating, provide
a
considerable increase in the number of nuclei for phosphate crystallization.
This is termed
activation of the phosphate coating formation." (Metal Finishing, v. 98, N 6,
2000, pp 57-73)
It is generally accepted in the art that without the first process of base
material
pickling (when the metal ions are transferred into the process solution),
creation of
phosphate conversion coating is extremely difficult or even impossible.
Therefore, these
types of coatings are widely applied on iron, iron pickled alloys and zinc,
and less on
aluminum Cd, Sn, Ag, Ti, Mn and their alloys. To apply phosphate conversion
coating on
non pickled materials is an extremely difficult or even impossible process.
Various attempts have been made to improve the PCC process, but each attempt
creates more problems. Some of these problems include: the need to heat the
materials to
high temperatures (e.g. up to ¨98 C), the need for very close monitoring of
the chemical
solution (usually sending samples to a lab for testing) and/or the need to
constantly correct
the chemical balance of the materials, expensive processes, the creation of
large amounts of
sludge (an environmental hazard in and of itself), the periodic need to halt
production lines
in order to clean out the treatment baths, the actual physically demanding
work of cleaning
out the baths and so on.
Efforts to reduce the dimensions of the phosphate coating crystals include
adding
chemical compounds into the refining suspension or phosphating solution,
applying
additional special baths, etc. All these techniques complicate the coating
line equipment,
technology and worsen the ecological aspects of the process.
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GLOSSARY OF ABBREVIATIONS
Ag - Silver
Ca - Calcium
Cd - Cadmium
PCC ¨ Phosphate Conversion Coatings
Fe ¨ Iron
Mn - Manganese
MOP ¨ Metal Oxide particles
Ni ¨Nickel
to PCCS - phosphate conversion coating solution
Sn - Tin
Ti - Titanium
Zn - Zinc
ZnO ¨ Zinc Oxide
ZPCCC ¨ Zinc Phosphate Conversion Crystal Coating
SUMMARY OF THE INVENTION
According to the present invention, the surfaces of the parts to be coated are
pretreated in a dry process of particle deposition on the surfaces before the
wet process of
treating the part with a phosphate coating solution.
The resulting process provides a universal procedure for coating all types of
substrates, both metallic and non-metallic. The process is greatly simplified
when compared
with coating processes currently known in the art. The phosphating solution is
also
simplified, obviating the need for various accelerants and additive chemicals.
Some of the main advantages of the immediate innovation over current processes
include:
a) The ability to form ultrafine crystalline conversion phosphate coating
structures of
required by customer thickness, where the coating has a high rate of adhesion
to substrate.
b) The ability to form conversion phosphate coating on any metal or alloy, as
well as
on nonmetallic substrates.
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c) Reducing phosphate conversion coating operating temperature (from the
norm).
For example, reducing the operational temperature for ZPCCC from between 40 C-
70 C to
30 C or less; reducing Manganese phosphate coating from about 90-98 C to 70 C
and less.
d) Reducing the number of pretreatment operations necessary before the actual
conversion phosphate coating operation.
e) Significantly reducing the volume of wastewater that is generated.
0 Significantly reducing the volume of sludge that is generated.
g) Using a simple composition of phosphate solution for the coating operation.
According to the present invention there is provided: A simple and stable
process; a
to phosphate solution that requires monitoring of only three parameters:
temperature, acidity
(pH) and density (each of these parameters can be controlled automatically);
and a closed-
loop process with no liquid wastes.
According to the present invention there is provided a method for providing
phosphate conversion crystal coating, the method including the steps of: pre-
treating a
substrate by depositing metal oxide particles on the substrate; treating the
substrate with a
phosphate coating solution, resulting in the phosphate conversion crystal
coating forming
(crystallizing) on the substrate.
According to further features in preferred embodiments of the invention
described
below crystallizing centers form at locations where the metal oxide particles
were deposited
prior to the treating of the substrate with the phosphate coating solution.
According to still further features in the described preferred embodiments the
metal
oxide particles are selected from the group including: CaO, ZnO, MnO, NiO and
combinations thereof.
According to still further features the metal oxide particles are deposited on
the
substrate in a quantity of between 0.5 and 100 g/m2.
According to still further features the largest dimension of any of the metal
oxide
particles is less than 2 gm.
According to still further features the phosphate coating solution comprises
oxides
diluted in phosphoric acid, the oxides selected from the group including:
Calcium Oxide,
Zinc Oxide, Manganese Oxide and combinations thereof.
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According to still further features the phosphate coating solution comprises
phosphates selected from the group including: Zinc Phosphates, Manganese
Phosphates,
Calcium Phosphates and mixtures thereof.
According to still further features the phosphate coating solution including
Zinc
5 Phosphates reacts with the metal oxide particles at a temperature of up
to 35 C.
According to still further features the phosphate coating solution including
Manganese Phosphates reacts with the metal oxide particles at a temperature of
up to 70 C.
According to still further features the phosphate coating solution has a pH
range of
between 2.2 and 2.7.
According to still further features the phosphate coating solution has a
phosphate
density of between 1.03 and 1.08 kg/l.
BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments are herein described, by way of example only, with
reference
to the accompanying drawings, wherein:
FIG. 1 is an image from an electron microscope of a prior art phosphate
conversion
coating;
FIG. 2 is an image from an electron microscope of a heavy Zinc phosphate
conversion coating using the immediate method;
FIG. 3 is an image from an electron microscope of a Zinc phosphate conversion
coating formed using the immediate method;
FIG. 4 is an image from an electron microscope of a cross-sectional view of
the
heavy Zinc phosphate conversion coating of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The principles and operation of a phosphate conversion coating process
according to
the present invention may be better understood with reference to the drawings
and the
accompanying description.
The present method is exemplarily illustrated using Zinc phosphate conversion
crystal coating (ZPCCC), although it is made clear that Calcium, Iron and
Manganese
phosphates can be used in place of, or in addition to, the Zinc phosphate.
Alternative or
additional materials are known in the art and included within the scope of the
invention.
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STATE OF THE ART FOR PHOSPHATE CONVERSION CRYSTAL COATING
As was described above, ZPCCC, as an example, is formed on a metal substrate
by
transforming phosphate ions and Zn ions from a liquid phase into a solid
phease on the
substrate surface of the treated parts. The process of phosphate conversion
crystal coating is
different from other well-known crystallization processes such as water
crystallization,
melted metal crystallization and the like. For example, water crystallization
depends solely
on physical changes: i.e. when the temperature drops, the water freezes.
By contrast, in order to form non-diluted Zn phosphate (i.e. crystals) from a
diluted
Zn phosphate, there is a need for a chemical process to take place. Chemical
processes
transform diluted one- and two-substituted Zn phosphate compounds into a non-
diluted
three-substituted Zn3(PO4)2 compound. These chemical processes require
suitable solution
acidity (pH level) and temperature. The suitable pH (usually higher than pH2)
level depends
on the composition of the solution. The temperature is controlled by
conventional heating
means. When the pH and the temperature of the solution reach the desired
critical levels, the
non-diluted Zn3(PO4)2 zinc phosphate compound forms spontaneously. The
compound
forms across the entire solution volume as a fine crystal white powder
precipitant.
The phenomenon of spontaneous formation of the fine crystal precipitant will
occur
within the entire solution volume, making the previously clear solution into a
murky
solution. More importantly, in such a case, the phosphate coating will not
form only on the
surfaces of the treated parts. This is obviously not desirable. On the other
hand, if the same
conditions of the solution are achieved only in a thin layer of solution above
the surface of
the treated substrate, then the phosphate coating will form on the substrate.
In order for the precipitant to only be created in a thin layer above the
surface of the
substrate ¨ and not in the entire solution ¨ the solution is engineered in
such a way that when
the solution comes into contact with the metal surface, the chemical reaction
of the metal
material and phosphoric acids in the solution results in the pH rising ¨ only
in the localized
area near the surface of the substrate ¨ and once the pH reaches a particular
level (e.g. 2.2),
and the suitable temperature is achieved, the conversion from soluble to non-
soluble occurs
and a PCC layer forms on the surface (in the immediate example, the PCC is a
Zinc PCC,
but alternative and/or additional phosphates can be used including Iron,
Manganese, Calcium
or mixtures thereof).
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The usual temperatures for such processes for forming heavy Zn and Mn
phosphate
coatings vary from 70 to 98 C. For thin phosphate coatings, it is possible to
reduce this
temperature to around 40 C for ZPCCC by adding additional components into the
phosphating solution.
This type of coating process, even with additional operations for refining the
phosphate crystals, still forms a coating with very coarse, flat crystal
structures. Typically,
the main crystals can reach dimensions of tens of microns. Referring now to
the drawings,
Figure 1 is an image from an electron microscope of a prior art phosphate
conversion
coating. (Source: Pragochem spol. s r.o) The image shows a structure of a
standard, heavy
Zinc phosphate conversion coating. As is evident from the image, the main
crystals have
dimensions on the scale of tens of microns.
Phosphate coatings with coarse crystalline structures have less effective
operating
characteristics. Liquids can penetrate the coating more easily between the
coarse structures,
reach the substrate surface and initiate its corrosion. Therefore, refining
these coating
structures and receiving coatings with finer structures, which are more
densely packed
together, are traditional goals in the development of new phosphate coating
technologies.
The dimensions (size) of the crystals of the phosphate coating depends on the
initial
concentration of crystallization centers and, consequently, the number of
areas where
crystals simultaneously start forming/growing. The more densly packed the
crystals are, the
smaller they are, as there is less room to grow before colliding with the
neighboring crystals.
One way of achieving more densely packed crystals is by seeding many
crystrillization
centers for the crystals start growing.
If there is any solid surface already in the solution volume, when the new
crystallization phase begins, the process of forming crystallization centers
on the solid
surfaces requires much less energy compared to the energy needed to create the
same
crystallization centers in the solution volume, further away from the solid
surface. Therefore,
it is possible to create the situation whereby the new crystal phase will form
on the solid
surface only (or almost exclusively), and not elsewhere in the solution
volume.
Furthermore, in order for crystals to form, the solution has to react with
something
which will trigger the crystallization phase. A metallic surface therefore
serves both to create
the reaction (transformation from diluted to non-diluted) and is also the best
place on which
the crystals can form.
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To summarize: The forming of phosphate coatings with required properties needs
two main chemical processes.
(1) Pickling of the substrate metal in the phosphating solution.
(2) Simultaneous creation of many crystallization centers on the substrate
surface.
In practice, each of these processes is optimized separately. (1) The
substrate metal
pickling can be accelerated, for example, by increasing the temperature or by
increasing the
activity of the phosphate solution (e.g. by adding additional chemicals) or by
substituting a
less diluted substrate metal with a more pickled one.
(2) Stimulating the creation of the crystallization centers may be done by
immersion
to .. of the treated part into a water suspension including very fine solid
particles or by the
addition of such particles directly into the bath with the phosphating
solution.
The present innovative method, explained in detail below, includes a
pretreatment of
the substrate surface by depositing Zinc oxide (ZnO) on the surface. Other
metallic oxides
may be used in addition to, or instead of, the Zinc Oxide. Therefore it is
made clear that the
.. use of ZnO is merely exemplary and not intended to be limiting.
In the first step, any dry process is used to deposit, adhere, and/or adsorb
ultrafine
ZnO crystals on the surface of a target substrate. Innovatively, the target
substrate that is to
be treated can essentially be of any material, not only metal.
In the next step, the aforementioned target part is treated in a wet process
with a
.. solution for phosphate coating. The wet process can be, for example, an
immersion bath, or
solution spray and the like. The solution can even be at room temperature (in
contradistinction to the high temperatures needed in contemporary methods).
The active
chemical reaction starts immediately.
Importantly, the chemical reaction occurs on the surface of the piece of
material as
the ZnO reacts with free phosphoric acid in a thin adsorption layer on the
surface of the
substrate. That is to say that the chemical stability of mono- and di-
substituted phosphate
compositions reduce/react and transform into the non-soluble trisubstituted
phosphate. The
initial particles of trisubstituted phosphate present as crystallizing centers
for non-stable
mono- and disubstituted phosphate complexes on which these non-stable
complexes are
transformed into the non-soluble trisubstituted phosphate and on which the
phosphate
crystals grow. The number of such crystal centers depends on the concentration
of ZnO
particles on the treated surface. The phosphate crystals are prevented from
growing overly
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large by increasing the number of crystal centers. Therefore, the higher the
concentration of
ZnO particles on the surface, the more densely packed the crystals will be and
hence the
finer the crystals will be.
Other oxides, metals, alloys or other chemical compounds react in the same or
similar manner. Generally, fine particles of such materials have to be fixedly
adhered on the
surface of the treated material. These particles may function as crystallizing
centers for
trisubstituted phosphate of Zinc, Manganese and/or Calcium.
Innovative Process
The present innovative method supposes to deposit solid particles of oxides,
metals,
alloys or other chemical compounds on the surface that is to be treated,
before initiating the
phosphate conversion coating process (e.g. before inserting the metal part
into the coating
bath or before spraying the coating solution onto the target part). As
mentioned, the particles
function as crystallizing centers for trisubstituted phosphate of Zinc,
Manganese and/or
Calcium.
As mentioned above, the method includes pretreating a target part by
depositing ultra
fine ZnO crystals on the surface of the target part (using any deposition
method). Once
pretreated, the target part is exposed to the phosphate conversion coating
solution (usually by
immersing the part in the solution, although the immediate method is not
limited to
immersion). The solution may even be at room temperature. The active chemical
reaction
will start immediately.
In order for the aforementioned process to work, the solid particles need to
meet the
following conditions: (1) The particles must be sufficiently small (e.g. from
a fraction of a
micron up to preferably 2 microns in size, referred to herein as ultra-fine
particles); and (2)
the particles must be able to adhere or attach to the surface of the substrate
in a sufficiently
strong manner.
The first condition may be realized by simply acquiring particles in the
preferred size
range. For example, the pretreatment particles can be ultrafine ZnO particles
of between 0.5
and 2 microns. One of the simplest and cheapest methods for particle
deposition or causing
the particles to be adsorbed on the part is to use particle deposition from an
aerosol, which is
a colloid of fine solid particles in air or another gas. The part is placed
into such a colloid, to
adsorb the aerosol particles. The concentration of the particles on the
surface depends on the
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concentration of particles in the aerosol and on the period of treatment
(dwelling time). The
longer the piece of material stays in the aerosol, the more particles settle
on the surface.
One exemplary apparatus for making such as aerosol is fluidized bed aerosol
generator, such as Fluidized Bed Aerosol Generator 3400a, manufactured by TSI
Inc. St.
5 Paul, Minnesota, USA. The generator contains a fluidized bed chamber and a
powder
reservoir. The fluidized bed consists of 100-pin bronze beads supported by a
porous screen
that allows clean, dry air to pass through, yet prevents the passage of any
powder. The air or
other gas is pumped from the bottom of the chamber through the powder layer.
The powder
particles are dispersed by the gas and create the aerosol in the cavity above
the powder layer.
to The best advantages of the aforementioned exemplary aerosol
generator are stable output
and concentration.
The second condition is also easily realized. The surface of each of the
treated parts
is usually coarse and activated enough with chemical bonds, such as metallic
bonds and
Van-der-Waals forces, for small particles to collect and adhere to the
surface. If the volume
of particle adhesion is insufficient, the treated surface can be mechanically
activated. In
addition, the surfaces of the small solid particles are also active, due to
their small
dimensions. These two factors provide for sufficiently high adhesion of any
adsorbed /
deposited particles.
PHOSPHATING SOLUTION ¨ STATE OF THE ART
Regular phosphate conversion coating liquids known in the art usually contain
several additional components, besides for the (PO4)3 anions and Zn+2 (or
similar) cations.
One exemplary known chemical composition of such a solution, which is fairly
typical in the
art, has the following composition:
Component Type of component Concentration range, g/1
Zn+2 Cations 0.5 ... 2
(PO4)3 Anions 10 ... 20
(NO3)- Anions 1 ... 30
Ni+2 Cations 0.5 ... 2
Co+2 Cations 0.5 ... 2
The acidity range of this solution is pH 2-3 and the temperature range is 40-
70 C.
The serious pollutants and heavy metals are clearly evident. Other processes
known
in the art further or alternatively include different organic compounds. The
complex
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chemical compositions known in the art, which also include undesirable
compounds, suffer
from many drawbacks in real world production. Some of these problems include:
a) The need for frequent laboratory testing of the phosphate solution chemical
composition.
b) The need for frequent phosphate solution chemical composition correction.
c) The solutions contain ions such as Ni+2, Co+2, (NO3)- etc. as well as
poisonous and/or
hazardous organic components which require additional expensive equipment for
pollution prevention and waste treatment as well as staff safety provisions.
d) The relatively high operational temperature of the phosphating conversion
coatings
to liquids
baths, even up to about 97 C. A great amount of energy is needed to maintain
such a high operational temperature, which in turn increases expenses, as well
as
additional expenses for safety-provisions, all the while contributing to the
greenhouse
effect and the like.
e) One of the specific, well-known problems is a huge volume of sludge.
PHOSPHATING SOLUTION ¨ PRESENT INNOVATION
By contrast, the immediate innovative process for pretreating surfaces with
metal
oxide particles (MOP) significantly reduces the operational temperature needed
for forming
the phosphate conversion coating and simplifies the chemical composition of
the PCCS.
The aforementioned particles are the basic components necessary for conversion
phosphate coating forming. Due to the high chemical activity of the material
particles with
the phosphate conversion coating solution (PCCS), there is no need for the
substrate itself to
chemically react with the solution (i.e. no need for substrate pickling), nor
is there a need for
elevated temperatures to realize the formation phosphate conversion coating.
For example,
the chemical reaction of ZnO with (PO4)-3 ions from the solution occurs even
at room
temperature.
When the phosphating solution reacts with the deposited aerosol particles, the
pH of
the PCCS increases at the interface layer. The increase in solution pH is
sufficient for: the
creation of non-soluble phosphate conversion coating compound, growth of the
crystalizing
centers and formation of the phosphate conversion coating on the treated
substrate.
The entire process is accomplished without necessarily pickling the substrate
material. As such, there is no need for adding any coating-forming
acceleration compounds
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into the solution. Therefore, the phosphoting solution is greatly simplified,
without having
the need for any unnecessary and/or dangerous chemicals.
Furthermore, according to the immediate innovative process, it is possible to
form
phosphate conversion coating on surfaces of materials which do not,
themselves, react with
PCCS, such as stainless steels, titanium alloys, plastics, glass etc.
The resulting simple chemical composition of PCCS is very easily controlled.
Only
two solution parameters, besides for the temperature, have to be controlled
and corrected: 1.
solution density and 2. solution pH. The properties of the coatings that are
formed can be
varied by varying these parameters. Experiments have shown that by varying the
Zinc PCCS
density between 1.03 and 1.08 kg/1, it is possible to form Zinc phosphate
conversion coating
with a thickness (measured in weight) ranging between 3 and 60 g/m2 where the
pH is
constant at approximately 2.55. Alternatively, while keeping the density
constant at 1.06
kg/1 and varying the pH of the solution between 2.2 and 2.7, the coating
thickness varies
between 4 and 40 g/m2, when the solution is at a temperature of 30 C.
In preferred embodiments, the phosphate coating solution has a pH range of
between
2.2 and 2.7. In preferred embodiments the phosphate coating solution has a
phosphate
density of between 1.03 and 1.08 kg/l.
In preferred embodiments, the metal oxide particles used in the pretreatment
of the
substrate are selected from the group including: CaO, ZnO, MnO, NiO and
combinations
thereof.
In preferred embodiments, metal oxide particles are deposited on the substrate
in a
quantity of between 0.5 and 100 g/m2. The greater the quantity of metal oxide
particles that
are deposited, the larger the number of crystallizing centers that form on the
substrate. The
more crystallizing centers, the more crystals form and, as a result, the
smaller the crystal
size/dimension. In preferred embodiments, the largest dimension of any of the
metal oxide
particles is less than 2 gm.
In preferred embodiments, the phosphate coating solution comprises oxides
diluted in
phosphoric acid. Preferably the oxides are selected from the group including:
Calcium
Oxide, Zinc Oxide, Manganese Oxide and combinations thereof.
Preferably the phosphate coating solution comprises phosphates. These
phosphates
are preferably selected from the group of: Zinc Phosphates, Manganese
Phosphates, Calcium
Phosphates and mixtures thereof. In one embodiment, where the phosphate
coating solution
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comprises Zinc phosphates, the solution reacts with the metal oxide particles
on the pre-
treated substrate at a temperature of up to 35 C. In another embodiment, where
the
phosphate coating solution comprises Manganese Phosphates, the solution reacts
with the
metal oxide particles at a temperature of up to 70 C.
Figure 2 is an image from an electron microscope of a heavy Zinc phosphate
conversion coating using the immediate method. In contrast to the crystals of
the prior art
coating, the crystals formed using the immediate invention have much smaller
dimensions.
In FIG. 2 the structure of present invention Zinc Phosphate conversion coating
has a
thickness (measured by weight) of 15 g/m2. The dimensions of the crystals are
measured on
a scale of 5 microns. It is clear from the image that the main crystals are
only, at the most,
several microns in size. Exemplary measurements, taking from FIG. 2, show
crystals
between about 2 ¨ 9 microns. As mentioned, these dimensions are merely
exemplary and not
intended to be limiting (on either side of the spectrum). Even the biggest
phosphate crystals
are about 10 times finer than crystals in coating formed using processes known
in the art (see
for example FIG. 1).
As the coating thickness increases, the phosphate crystals grow. Therefore the
crystal
in thinner coatings will have smaller dimensions. Figure 3 is another image
from an electron
microscope of a Zinc phosphate conversion coating formed using the immediate
method.
The displayed Zinc Phosphate conversion coating is thinner than the coating of
FIG. 2,
having a thickness of 6 g/m2. In FIG. 3 the dimensions of the crystals are
measured on a
scale of one micron. It is evident that the main crystals are less than a
micron in size. In the
exemplary image, measurements are between about 0.2 ¨ 3 microns. As mentioned,
these
dimensions are merely exemplary and not intended to be limiting (on either
side of the
spectrum).
Figure 4 is an image from an electron microscope of a cross-sectional view of
the
heavy Zinc phosphate conversion coating of FIG. 2. The thickness of the
coating, measured
in weight, is 15 g/m2. The good adhesion of the coating crystals with the
substrate surface
gives a result of the very solid and uniform coating structure with minimal
non-coated
substrate surface areas (e.g. as seen in FIG. 4). The inventive coating is
using as a pre-
treatment for subsequent coating of the part with paints, topcoats, rubber and
plastic
moldings. The good adhesion between the coating and the substrate also
provides the good
adhesion for the top coatings, paint, protective coatings, rubber, plastic
etc. to the substrate.
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The present invention successfully addresses all of the drawbacks and
deficiencies of
the phosphate conversion coating processes known in the art. The PCCS
according to the
present invention has higher stability than similar solutions known in the art
and is
minimally hazardous for both the workers and the environment. The operational
parameters
of the solution are also easy corrected. For example, the parameters of the
solution can be
corrected by adding the required quantity of PCCS concentrate containing (PO4)-
3 and Zn+2,
Mn+2 or Ca+2 ions, depending on type of conversion coating.
In experiments, the following equipment was used:
1. A fluidized bed aerosol generator was used. The generator value is
¨0.3m3
and operation value ¨0.25m3. The quantity of modification material varied from
0.1 to 3 kg,
for varying aerosol concentrations. The optimal period for surface
modification of the treated
samples was found to be three minutes.
2. The concentration of deposited aerosol particles was measured by
weighing
the treated samples before and after deposition. A semi-analytical scale by
Ragway
Company, Poland, having an accuracy of 0.001g was used for weighing samples.
3. The density of the solutions was measured with suitable hydrometers have
an
accuracy of 0.01 kg/l.
4. The acidity of the solutions was measured with a Milwaukee pH-meter P-
600,
by Milwaukee Instruments, Inc., Rocky Mount, NC, USA, with glass electrode,
having an
accuracy of 0.01.
5. The phosphate coating thickness on the treated samples was measured by
weighing of the coated samples after coating and after coating stripping
according the MIL-
DTL-16232G specification.
6. The test samples were produced from 1020 steel, 101 copper, 316
stainless
steel, 2014 aluminum alloy, polypropylene, annealed glass.
While the invention has been described with respect to a limited number of
embodiments, it will be appreciated that many variations, modifications and
other
applications of the invention may be made. Therefore, the claimed invention as
recited in
the claims that follow is not limited to the embodiments described herein.
Date Recue/Date Received 2020-05-19
